1. Field of Use
This invention relates generally to crawler shoes used in crawler tracks for mining shovels or other heavy-duty equipment and to methods for making such crawler shoes.
2. Description of the Prior Art
The crawler shoes of crawler tracks used in heavy-duty equipment such as mining shovels are subjected to wear and tear resulting from operation in dust, mud, and highly abrasive soils, shock loads, and other severe operating conditions. Adjacent shoes in a crawler track are connected to one another by means of removable, replaceable pins which permit articulation of adjacent shoes and also enable shoes to be replaced as they become worn. Such crawler shoes are relatively large, being on the order of up to five feet wide, for example, and heretofore have been made by casting alloy steel. In a typical crawler track, heavy-duty forged or cast alloy steel rollers ride upon the upper surface of each shoe and transfer crushing loads thereto from the heavy machinery thereabove. The life of crawler shoes can be extended by using different metals having desired properties and by designing the shoe to achieve desired load distribution thereacross. Even so, operating conditions are very severe and such shoes must be frequently replaced. Such shoes are very expensive and downtime on the machine and labor costs result in additional expense during shoe replacement.
Heretofore, crawler shoes for mining shovels were manufactured by casting and, to reduce weight, had hollow cores or chambers on the interior thereof. Such construction posed serious problems during manufacture of the shoes. For example, sand in which the shoe was cast burned into the casting on the exterior and interior surfaces thereof causing defects. Furthermore, because the castings were large, shrinkage of the metal and cracking occurred as the casting cooled creating flaws and undesirable internal stresses which weakened the shoe and imposed the risk of damage or breakage during use. Also, shifting of the internal cores during the casting process caused variations in metal thickness thereby producing weak points. Furthermore, in shoes formed by casting, it is necessary for the same material to be used throughout a single cast piece even though material requirements such as strength, hardness, ductility, and toughness vary from one area to another on the shoe, depending on the type of loads and operating conditions imposed on the shoes during operation. The prior art contains many examples of attempts to design and fabricate track shoes which overcome the aforementioned and other problems. For example, U.S. Pat. No. 3,477,769 discloses a crawler shoe which is fabricated of numerous sub-components each made of a material having certain desirable properties and wherein the several components are secured together by means of large bolts.